Offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (das)

ABSTRACT

Offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS) is disclosed. In this regard, in one example, an interference signal offset circuit is provided in an RAU to offset intermodulation products leaked from a downlink path to an uplink path. An offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the intermodulation products leaked from the downlink path. A signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink signal received on the uplink path, thus offsetting the intermodulation products in the uplink signal. By providing the interference signal offset circuit in the RAU to offset the intermodulation products on the uplink path, it is possible to provide more implementation flexibility for the RAU without degrading the uplink signal.

PRIORITY APPLICATION

This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application No. 62/118,186, filed on Feb. 19, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates generally to distribution of communications signals in a distributed antenna system (DAS), and more particularly to offsetting unwanted downlink interference signals in an uplink path in a DAS resulting from a shared antenna for downlink and uplink communication in a remote antenna unit (RAU).

Wireless customers are increasingly demanding digital data services, such as streaming video signals. Concurrently, some wireless customers use their wireless devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs can be particularly useful when deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source. DASs include RAUs configured to receive and transmit communications signals to client devices within the antenna range of the RAUs.

A typical DAS comprises head-end equipment (HEE) communicatively coupled to a plurality of RAUs. The HEE is connected to receive a variety of wireless services for distribution to the RAUs, such as wideband code division multiple access (WCDMA), long term evolution (LTE), and wireless local area network (WLAN) communications services as examples. To distribute such wireless communications services in a DAS, the wireless communications services can be provided in the form of analog RF communications signals and/or digital communications signals to the HEE of the DAS for distribution to the RAUs.

An RAU in the DAS may be configured to support more than one type of wireless service that operates in a variety of RF spectrums and bandwidths. Downlink wireless communications signals received by the RAU are typically amplified by a power amplifier to increase the signal strengths before distributing the downlink wireless communications signals to client devices through one or more coupled antennas. However, the amplified downlink communications signals may comprise a plurality of intermodulation products. For example, these intermodulation products may be created as a result of non-linearities of the power amplifier in the downlink path. For instance, if two downlink wireless communications signals operating on 850 MegaHertz (MHz) and 870 MHz bands, respectively, are amplified by a power amplifier, a plurality of intermodulation products may be generated below the 850 MHz band (e.g., 830 MHz, 810 MHz, 790 MHz, and so on) and above the 870 MHz band (e.g. 890 MHz, 910 MHz, 930 MHz, and so on). Hence, the intermodulation products should be sufficiently isolated to prevent or reduce interferences on adjacent wireless communication channels.

No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.

SUMMARY

One embodiment of the disclosure relates to offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS). In DASs disclosed herein, at least one remote antenna unit (RAU) is provided. The RAU is configured to receive downlink wireless communications signals in a downlink path and distribute the downlink wireless communications signals to one or more client devices through a coupled antenna. The RAU is also configured to receive “wanted” uplink wireless communications signals from the one or more client devices on an uplink path through the coupled antenna and distribute the uplink wireless communications signals on the uplink path. By “wanted” uplink wireless communications signals, it means that these uplink wireless communications signals are received from the one or more client devices to be distributed in the DAS. Intermodulation products of the downlink wireless communications signals can be generated in the downlink path and leak over to the uplink path, thus interfering with the uplink wireless communications signals and degrading the uplink wireless communications signals. Thus, these one or more intermodulation products are interferences that may degrade the “wanted” uplink wireless communications signal and thus are “unwanted” downlink interference signals that are desired to be suppressed. For example, a downlink power amplifier that amplifies downlink wireless communications signals before the downlink wireless communications signals are distributed to client devices may generate one or more intermodulation products of the downlink wireless communications signals.

In this regard, in DASs disclosed herein, an interference signal offset circuit is provided. The interference signal offset circuit can be associated with the RAU. The interference signal offset circuit is configured to offset the plurality of downlink intermodulation products on the uplink signal path. The interference signal offset circuit comprises at least one offset signal generation circuit and a signal summing circuit. The offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the plurality of intermodulation products associated with the downlink path. The signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink wireless communications signals received on the uplink path, thus offsetting the plurality of leaked intermodulation products in the uplink wireless communications signals. By providing the interference signal offset circuit in the RAU to offset the plurality of leaked intermodulation products on the uplink path, it is possible to provide more flexibility in implementation for the RAU without degrading the uplink wireless communications signals.

An additional embodiment of the disclosure relates to an interference signal offset circuit in a DAS. The interference signal offset circuit comprises at least one offset signal generation circuit. The at least one offset signal generation circuit is configured to receive a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The at least one offset signal generation circuit is also configured to generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The interference signal offset circuit also comprises a signal summing circuit. The signal summing circuit is configured to receive an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path. The signal summing circuit is also configured to receive the at least one uplink interference offset signal. The signal summing circuit is also configured to generate an output uplink signal based on the received uplink signal. The signal summing circuit is also configured to combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal. The interference signal offset circuit also comprises a control circuit. The control circuit is configured to receive the output uplink signal from the signal summing circuit. The control circuit is also configured to configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.

An additional embodiment of the disclosure relates to a method of offsetting at least one unwanted downlink interference signal from an uplink signal received in a DAS. The method comprises receiving a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The method also comprises generating at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The method also comprises receiving an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path. The method also comprises generating an output uplink signal based on the uplink signal. The method also comprises combining the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal.

An additional embodiment of the disclosure relates to an RAU in DAS. The RAU comprises a downlink power amplifier configured to amplify a plurality of downlink communications signals received in a downlink path to generate a downlink signal in the downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The RAU also comprises an antenna configured to transmit the downlink signal and receive an uplink signal. The RAU also comprises a coupling device communicatively coupled to the downlink power amplifier and the antenna. The coupling device is configured to provide the downlink signal received from the downlink path to the antenna for transmission. The coupling device is also configured to provide the uplink signal received from the antenna to an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path.

The RAU also comprises an interference signal offset circuit. The interference signal offset circuit comprises at least one offset signal generation circuit. The at least one offset signal generation circuit is configured to receive the downlink signal comprising the at least one unwanted downlink interference signal. The at least one offset signal generation circuit is also configured to generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The interference signal offset circuit also comprises a signal summing circuit. The signal summing circuit is configured to receive the uplink signal in the uplink path. The signal summing circuit is also configured to receive the at least one uplink interference offset signal from the at least one offset signal generation circuit. The signal summing circuit is also configured to generate an output uplink signal based on the received uplink signal and the received at least one uplink interference offset signal. The signal summing circuit is also configured to combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal. The interference signal offset circuit also comprises a control circuit. The control circuit is configured to receive the output uplink signal from the signal summing circuit. The control circuit is also configured to configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary distributed antenna system (DAS);

FIG. 2 is a schematic diagram of an exemplary interference signal offset circuit that can be provided in a DAS, wherein the interference signal offset circuit comprises at least one offset signal generation circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path;

FIG. 3 is flowchart of an exemplary interference signal offset process performed by the interference signal offset circuit in FIG. 2 for offsetting the at least one unwanted downlink interference signal in an uplink path;

FIG. 4 is a schematic diagram of another exemplary interference signal offset circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path, based a first operation configuration to measure a first power level and a first phase of at least one downlink test intermodulation product;

FIG. 5 is a schematic diagram of another exemplary interference signal offset circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path, based a second operation configuration to measure a second power level and a second phase of at least one downlink intermodulation product;

FIG. 6 is a schematic diagram of an exemplary optical fiber-based DAS that may include one or more interference signal offset circuits to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; and

FIG. 7 is a partially schematic cut-away diagram of an exemplary building infrastructure in which an interference signal offset circuit, including the interference signal offset circuits of FIGS. 2, 4, and 5 can be employed.

DETAILED DESCRIPTION

One embodiment of the disclosure relates to offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS). In DASs disclosed herein, at least one remote antenna unit (RAU) is provided. The RAU is configured to receive downlink wireless communications signals in a downlink path and distribute the downlink wireless communications signals to one or more client devices through a coupled antenna. The RAU is also configured to receive “wanted” uplink wireless communications signals from the one or more client devices on an uplink path through the coupled antenna and distribute the uplink wireless communications signals on the uplink path. By “wanted” uplink wireless communications signals, it is meant that these uplink wireless communications signals are received from the one or more client devices to be distributed in the DAS. Intermodulation products of the downlink wireless communications signals can be generated in the downlink path and leak over to the uplink path, thus interfering with the uplink wireless communications signals and degrading the uplink wireless communications signals. Thus, these one or more intermodulation products are interferences that may degrade the “wanted” uplink wireless communications signal and thus are “unwanted” downlink interference signals that are desired to be suppressed. For example, a downlink power amplifier that amplifies downlink wireless communications signals before the downlink wireless communications signals are distributed to client devices may generate one or more intermodulation products of the downlink wireless communications signals. In this regard, in DASs disclosed herein, an interference signal offset circuit is provided. The interference signal offset circuit can be associated with the RAU. The interference signal offset circuit is configured to offset the plurality of downlink intermodulation products on the uplink signal path. The interference signal offset circuit comprises at least one offset signal generation circuit and a signal summing circuit. The offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the plurality of intermodulation products associated with the downlink path. The signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink wireless communications signals received on the uplink path, thus offsetting the plurality of leaked intermodulation products in the uplink wireless communications signals. By providing the interference signal offset circuit in the RAU to offset the plurality of leaked intermodulation products on the uplink path, it is possible to provide more flexibility in implementation for the RAU without degrading the uplink wireless communications signals.

Before discussing examples of offsetting unwanted downlink interference signals in an uplink path in a DAS starting at FIG. 2, a discussion of an exemplary DAS that employs a communications medium to support wireless communications services to a plurality of RAUs is first provided with reference to FIG. 1. The discussion of specific exemplary aspects of offsetting unwanted downlink interference signals in an uplink path in a DAS starts at FIG. 2.

In this regard, FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as radio frequency (RF) identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas 10(1)-10(N) may be remotely located. In this regard, the remote coverage areas 10(1)-10(N) are created by and centered on RAUs 14(1)-14(N) connected to a head-end equipment (HEE) 16 (e.g., a head-end controller or head-end unit or central unit). The HEE 16 may be communicatively coupled to a signal source 18, for example a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the HEE 16 receives downlink communications signals 20D from the signal source 18 to be distributed to the RAUs 14(1)-14(N). The RAUs 14(1)-14(N) are configured to receive the downlink communications signals 20D from the HEE 16 over a communications medium 22 to be distributed to the respective coverage areas 10(1)-10(N) of the RAUs 14(1)-14(N). In a non-limiting example, the communications medium 22 may be a wired communications medium, a wireless communications medium, or an optical fiber-based communications medium. Each of the RAUs 14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna 24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective remote coverage areas 10(1)-10(N). The RAUs 14(1)-14(N) are also configured to receive uplink communications signals 20U from the client devices 26 in their respective remote coverage areas 10(1)-10(N) to be distributed to the signal source 18. The size of a given remote coverage area 10(1)-10(N) is determined by the amount of RF power transmitted by the respective RAU 14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the client device 26. Client devices 26 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the RAUs 14(1)-14(N) mainly determine the size of their respective remote coverage areas 10(1)-10(N).

With reference to FIG. 1, the downlink communications signals 20D and the uplink communications signals 20U may be distributed on adjacent downlink and uplink channels (not shown). For example, the downlink communications signals 20D may be distributed on an 850-870 MegaHertz (MHz) downlink channel and the uplink communications signals 20U may be distributed on an 825-845 MHz uplink channel. The RF transmitter/receiver in each of the RAUs 14(1)-14(N) is connected to the respective antenna 24(1)-24(N) through a coupling device (not shown). The coupling device is configured to alternate between transmitting the downlink communications signals 20D to the respective antennas 24(1)-24(N) and receiving the uplink communications signals 20U from the respective antennas 24(1)-24(N). The downlink communications signals 20D are amplified at each of the RAUs 14(1)-14(N) by a downlink power amplifier (not shown) to increase the signal strength prior to being provided to the coupling device. Due to non-linearities of the downlink power amplifier, a plurality of intermodulation products 28(1)-28(X) may be generated and associated with the amplified downlink communications signals 20D. In this regard, the plurality of intermodulation products 28(1)-28(X) may be leaked to an uplink path 29 due to insufficient isolation by the coupling device, thus degrading the uplink communications signals 20U. One solution for preventing these intermodulation products 28(1)-28(X) from leaking into the uplink path 29 is to employ high isolation RF filters (e.g., cavity filters) in the coupling device. However, the high isolation RF filters may lead to significant cost increase of the RAUs 14(1)-14(N). However, it may be desirable to avoid using higher cost high isolation RF filters in the RAUs 14(1)-14(N) due to their significant costs.

In this regard, FIG. 2 is a schematic diagram of an exemplary interference signal offset circuit 30. The interference signal offset circuit 30 includes an offset signal generation circuit 32. The offset signal generation circuit 32 is configured to generate at least one uplink interference offset signal 34 in an uplink path 40 to offset at least one unwanted downlink interference signal 36 leaked from a downlink path 38 to an uplink path 40. In this regard, the offset signal generation circuit 32 receives a downlink signal 42 in the downlink path 38. The downlink signal 42 is an amplified downlink signal 42 generated by a downlink power amplifier 44 based on a plurality of downlink communications signals 46(1)-46(M). Due to non-linearities of the downlink power amplifier 44, the downlink signal 42 may comprise the at least one unwanted downlink interference signal 36 after being amplified by the downlink power amplifier 44. In a non-limiting example, the at least one unwanted downlink interference signal 36 comprises a plurality of downlink intermodulation products 48(1)-48(N) generated by the downlink power amplifier 44. The plurality of downlink intermodulation products 48(1)-48(N) are additional downlink signals formed at frequencies different from the downlink signal 42. For example, if the downlink power amplifier 44 received two downlink communications signals 46(1), 46(2) operating on 850 MHz and 870 MHz bands, respectively, the plurality of downlink intermodulation products 48(1)-48(N) may exist at 830 MHz, 810 MHz, 790 MHz, and so on, as well as at 890 MHz, 910 MHz, 930 MHz, and so on.

With continuing reference to FIG. 2, the downlink signal 42 and the at least one unwanted downlink interference signal 36 are also received by a coupling device 50 and distributed to one or more client devices (not shown) via at least one antenna 52 that is communicatively coupled to the coupling device 50. The coupling device 50 also receives a wanted uplink signal 54 from the one or more client devices via the antenna 52 and provides the received wanted uplink signal 54 to the uplink path 40. Accordingly, the coupling device 50 is configured to alternate between transmitting the downlink signal 42 and receiving the wanted uplink signal 54. In a non-limiting example, the coupling device 50 may be a duplexer, a multiplexer, a hybrid combiner, or a software-defined frontend module. In another non-limiting example, the coupling device 50 may be a lower-cost ceramic filter that is unable to sufficiently isolate the at least one unwanted downlink interference signal 36. As a result, the at least one unwanted downlink interference signal 36 may be leaked from the downlink path 38 to the uplink path 40. Consequently, the coupling device 50 provides an uplink signal 54′, which comprises the wanted uplink signal 54 and the at least one unwanted downlink interference signal 36, to the uplink path 40. In this regard, the wanted uplink signal 54 is generated by the one or more client devices for distribution on the uplink path 40. In contrast, the at least one unwanted downlink interference signal 36 is introduced by an interferer such as the downlink power amplifier 44, thus must not be distributed on the uplink path 40.

With continuing reference to FIG. 2, the interference signal offset circuit 30 also comprises a signal summing circuit 56. The signal summing circuit 56 is configured to receive the uplink signal 54′ in the uplink path 40 from the coupling device 50 and generate an output uplink signal 58 based on the uplink signal 54′. In this regard, the output uplink signal 58 is the same as the uplink signal 54′. The signal summing circuit 56 is communicatively coupled to the offset signal generation circuit 32 to receive the at least one uplink interference offset signal 34. The signal summing circuit 56 is configured to combine the at least one uplink interference offset signal 34 with the uplink signal 54′. As is further discussed in FIGS. 4 and 5, the at least one uplink interference offset signal 34 is configured to have a matching power level and an opposing phase as the at least one unwanted downlink interference signal 36 comprised in the uplink signal 54′. In this regard, the at least one unwanted downlink interference signal 36 is offset by the at least one uplink interference offset signal 34 when the signal summing circuit 56 combines the at least one uplink interference offset signal 34 with the uplink signal 54′. Hence, the output uplink signal 58′ comprises only the wanted uplink signal 54.

With continuing reference to FIG. 2, note that the offset signal generation circuit 32 illustrated herein may comprise a plurality of offset signal generation circuits 32 disposed in a parallel arrangement. Each of the plurality of offset signal generation circuits 32 may be configured to generate the at least one uplink interference offset signal 34 to offset at least one downlink intermodulation product among the plurality of downlink intermodulation products 48(1)-48(N). In this regard, the plurality of offset signal generation circuits 32 generates a plurality of uplink interference offset signals 34, respectively.

With continuing reference to FIG. 2, the interference signal offset circuit 30 also comprises a control circuit 60 communicatively coupled to the offset signal generation circuit 32 and the signal summing circuit 56. In this regard, the control circuit 60 is configured to receive the output uplink signal 58. As is further discussed in FIGS. 4 and 5, the control circuit 60 measures an interference signal power level and an interference signal phase of at least one downlink intermodulation product among the plurality of downlink intermodulation products 48(1)-48(N). Based on the measured interference signal power level and the measured interference signal phase, the control circuit 60 then configures the offset signal generation circuit 32 to generate the at least one uplink interference offset signal 34. The at least one uplink interference offset signal 34 then offsets the at least one unwanted downlink interference signal 36.

In this regard, FIG. 3 is flowchart of an exemplary interference signal offsetting process 70 for offsetting the at least one unwanted downlink interference signal 36 in FIG. 2 in the uplink path 40. With reference to FIG. 3, the downlink signal 42 is received in the downlink path 38, wherein the downlink signal 42 comprises the at least one unwanted downlink interference signal 36 (block 72). Next, the at least one uplink interference offset signal 34 is generated based on the received at least one unwanted downlink interference signal 36 (block 74). The uplink signal 54′ is received in the uplink path 40, wherein the uplink signal 54′ comprises the wanted uplink signal 54 and the at least one unwanted downlink interference signal 36 that is leaked from the downlink path 38 to the uplink path 40 (block 76). Subsequently, the output uplink signal 58 is generated based on the uplink signal 54′ (block 78). In this regard, the output uplink signal 58 comprises the wanted uplink signal 54 and the at least one unwanted downlink interference signal 36. Finally, the at least one uplink interference offset signal 34 is combined with the uplink signal 54′ to offset the at least one unwanted downlink interference signal 36 in the output uplink signal 58′ (block 80).

As previously mentioned in FIG. 2, the control circuit 60 configures the offset signal generation circuit 32 to generate the at least one uplink interference offset signal 34 to offset the at least one unwanted downlink interference signal 36. In fact, the control circuit 60 takes two steps to configure offsetting the at least one unwanted downlink interference signal 36. In the first step, the control circuit 60 configures the interference signal offset circuit 30 based on a first operation configuration. In the second step, the control circuit 60 configures the interference signal offset circuit 30 based on a second operation configuration. In this regard, FIGS. 4 and 5 illustrate the first operation configuration and the second operation configuration, respectively. Common elements between FIGS. 2, 4, and 5 are shown with common element numbers, and thus will not be re-described herein.

In this regard, FIG. 4 is a schematic diagram of an exemplary interference signal offset circuit 30(1) configured based on the first operation configuration to measure a first power level and a first phase of at least one downlink test intermodulation product 90. The interference signal offset circuit 30(1) comprises at least one offset signal generation circuit 32(1), a signal summing circuit 56(1), and a control circuit 60(1). The coupling device 50 is coupled to the antenna 52 by a first switch (S1) 92, which is kept in an open position in the first operation configuration. The signal summing circuit 56(1) comprises a second switch (S2) 94 and a third switch (S3) 96. The signal summing circuit 56(1) also comprises a signal summing point 98 coupled to the second switch (S2) 94 and the third switch (S3) 96. The signal summing point 98 is configured to combine the at least one uplink interference offset signal 34 with the uplink signal 54′.

With reference to FIG. 4, the coupling device 50 receives a downlink test signal 102 in the downlink path 38. The downlink test signal 102 is an amplified downlink test signal 102 generated by the downlink power amplifier 44 based on a plurality of downlink test communications signals 104(1)-104(M). In a non-limiting example, the plurality of downlink test communications signals 104(1)-104(M) may be generated by a signal generator (not shown) coupled to the downlink power amplifier 44. The plurality of downlink test communications signals 104(1)-104(M) are in the same operating bands as the plurality of downlink communications signals 46(1)-46(M) (not shown). Alternatively, the downlink test signal 102 may also be generated based on the plurality of downlink communications signals 46(1)-46(M). Due to the non-linearities of the downlink power amplifier 44, the downlink test signal 102 comprises a plurality of downlink test intermodulation products 106(1)-106(N).

With continuing reference to FIG. 4, the coupling device 50 comprises a downlink signal filter 108 and an uplink signal filter 110. Given that the first switch (S1) 92 is kept open according to the first operation configuration, the downlink test signal 102 passes through the downlink signal filter 108 and becomes an uplink test signal 112 in the uplink path 40. The downlink signal filter 108, however, is unable to provide sufficient RF isolation to eliminate the plurality of downlink test intermodulation products 106(1)-106(N) comprised in the downlink test signal 102. As a result, the plurality of downlink test intermodulation products 106(1)-106(N) is leaked to the uplink path 40. Given that the third switch (S3) 96 is also kept open according to the first operation configuration, the at least one offset signal generation circuit 32(1) is decoupled from the signal summing point 98. Therefore, the uplink test signal 112, along with the plurality of downlink test intermodulation products 106(1)-106(N), is received by an uplink power amplifier 114 configured to amplify the uplink test signal 112.

With continuing reference to FIG. 4, the control circuit 60(1) comprises an uplink signal filter 116 coupled to the uplink power amplifier 114. The uplink signal filter 116 receives the uplink test signal 112 and selectively passes the at least one downlink test intermodulation product 90 among the plurality of downlink test intermodulation products 106(1)-106(N) that is comprised in the uplink test signal 112. A power detection circuit 118, coupled to the uplink signal filter 116, is configured to receive and measure the first power level of the at least one downlink test intermodulation product 90 passed through the uplink signal filter 116. Subsequently, a controller 120, coupled to the power detection circuit 118, receives the at least one downlink test intermodulation product 90 from the power detection circuit 118 and measures the first phase of the at least one downlink test intermodulation product 90.

FIG. 5 is a schematic diagram of an exemplary interference signal offset circuit 30(2) configured based on the second operation configuration to measure a second power level and a second phase of at least one downlink intermodulation product 130. According to the second operation configuration, the first switch (S1) 92 and the second switch (S2) 94 are kept open while the third switch (S3) 96 is closed. By opening the second switch (S2) 94, the coupling device 50 is decoupled from the signal summing point 98. By closing the third switch (S3) 96, at least one offset signal generation circuit 32(2) is coupled to the signal summing point 98.

With reference to FIG. 5, the at least one offset signal generation circuit 32(2) receives the downlink signal 42, which may comprise the plurality of downlink intermodulation products 48(1)-48(N). The at least one offset signal generation circuit 32(2) comprises an intermodulation product filter 132, an adjustable power amplifier 134, and an adjustable phase shifter 136. The intermodulation product filter 132 is controlled by the controller 120 to selectively pass the at least one downlink intermodulation product 130 to the adjustable power amplifier 134. In a non-limiting example, the at least one downlink intermodulation product 130 passed through the intermodulation product filter 132 is in the same order as the at least one downlink test intermodulation product 90. For instance, if the at least one downlink test intermodulation product 90 is a third order intermodulation product among the plurality of downlink test intermodulation products 106(1)-106(N), the at least one downlink intermodulation product 130 is also a third order modulation product among the plurality of downlink intermodulation products 48(1)-48(N).

With continuing reference to FIG. 5, the at least one downlink intermodulation product 130 passes through the adjustable power amplifier 134, the adjustable phase shifter 136, and the uplink signal filter 116 without being modified. The power detection circuit 118 measures the second power level of the at least one downlink intermodulation product 130. Subsequently, the controller 120 measures the second phase of the at least one downlink intermodulation product 130. Next, the controller 120 compares the second measured power level against the first measured power level. If the second measured power level is different from the first measured power level, the controller 120 then controls the adjustable power amplifier 134 to continuously adjust the second power level until the second power level substantially matches the first power level. Furthermore, the controller 120 controls the adjustable phase shifter 136 to phase-shift the second phase to be substantially opposite of the first phase. By having the second power level substantially match the first power level and the second phase substantially oppose the first phase, the at least one downlink intermodulation product 130 is able to offset the at least one downlink test intermodulation product 90. The interference signal offset circuit 30(2) is placed in a normal operation configuration by closing the first switch (S1) 92, the second switch (S2) 94, and the third switch (S3) 96. Hence, as illustrated earlier in FIG. 2, the at least one offset signal generation circuit 32 is able to generate the at least one uplink interference offset signal 34 to offset the at least one unwanted downlink interference signal 36.

The interference signal offset circuits 30, 30(1), and 30(2) in FIGS. 2, 4, and 5, respectively, can be provided in other DASs as well, without limitation. For example, FIG. 6 is a schematic diagram of exemplary optical fiber-based DAS 140 that may be employed according to the embodiments disclosed herein to include an interference signal offset circuit, like the interference signal offset circuit 30 in FIG. 2. In this embodiment, the optical fiber-based DAS 140 includes an optical fiber for distributing communications services. The optical fiber-based DAS 140 in this embodiment is comprised of three (3) main components. One or more radio interfaces, provided in the form of radio interface modules (RIMs) 142(1)-142(M) in this embodiment, are provided in a central unit 144 to receive and process downlink electrical communications signals 146D(1)-146D(R) prior to optical conversion into downlink optical communications signals. The RIMs 142(1)-142(M) provide both downlink and uplink interfaces. The notations “1-R” and “1-M” indicate that any number of the referenced component, 1-R and 1-M, respectively, may be provided. The central unit 144 is configured to accept the RIMs 142(1)-142(M) as modular components that can easily be installed and removed or replaced in the central unit 144. In one embodiment, the central unit 144 is configured to support up to twelve (12) RIMs 142(1)-142(12).

Each RIM 142(1)-142(M) can be designed to support a particular type of radio source or range of radio sources (i.e., frequencies) to provide flexibility in configuring the central unit 144 and the optical fiber-based DAS 140 to support the desired radio sources. For example, one RIM 142 may be configured to support the Personal Communication Services (PCS) radio band. Another RIM 142 may be configured to support a 700 MHz radio band. In this example, by inclusion of these RIMs 142, the central unit 144 could be configured to support and distribute communications signals on both PCS and Long Term Evolution (LTE) radio bands, as an example. The RIMs 142(1)-142(M) may be provided in the central unit 144 that support any frequency bands desired, including but not limited to the US Cellular band, Personal Communication Services (PCS) band, Advanced Wireless Services (AWS) band, 700 MHz band, LTE bands, Global System for Mobile communications (GSM) 900, GSM 1800, and Universal Mobile Telecommunication System (UMTS). The RIMs 142(1)-142(M) may also be provided in the central unit 144 that support any wireless technologies desired, including but not limited to Code Division Multiple Access (CDMA), CDMA200, 1×RTT, Evolution-Data Only (EV-DO), UMTS, High-speed Packet Access (HSPA), GSM, General Packet Radio Services (GPRS), Enhanced Data GSM Environment (EDGE), Time Division Multiple Access (TDMA), LTE, Integrated Digital Enhanced Network (iDEN), and Cellular Digital Packet Data (CDPD).

The RIMs 142(1)-142(M) may be provided in the central unit 144 that support any frequencies desired, including but not limited to US Federal Communications Commission (FCC) and Industry Canada frequencies (824-849 MHz on uplink and 869-894 MHz on downlink), US FCC and Industry Canada frequencies (1850-1915 MHz on uplink and 1930-1995 MHz on downlink), US FCC and Industry Canada frequencies (1710-1755 MHz on uplink and 2110-2155 MHz on downlink), US FCC frequencies (698-716 MHz and 776-787 MHz on uplink and 728-746 MHz on downlink), EU R & TTE frequencies (880-915 MHz on uplink and 925-960 MHz on downlink), EU R & TTE frequencies (1710-1785 MHz on uplink and 1805-1880 MHz on downlink), EU R & TTE frequencies (1920-1980 MHz on uplink and 2110-2170 MHz on downlink), US FCC frequencies (806-824 MHz on uplink and 851-869 MHz on downlink), US FCC frequencies (896-901 MHz on uplink and 929-941 MHz on downlink), US FCC frequencies (793-805 MHz on uplink and 763-775 MHz on downlink), and US FCC frequencies (2495-2690 MHz on uplink and downlink).

The downlink electrical communications signals 146D(1)-146D(R) are provided to a plurality of optical interfaces, provided in the form of optical interface modules (OIMs) 148(1)-148(N) in this embodiment, to convert the downlink electrical communications signals 146D(1)-146D(R) into downlink optical communications signals 150D(1)-150D(R). The notation “1-N” indicates that any number of the referenced component 1-N may be provided. The OIMs 148(1)-148(N) may be configured to provide one or more optical interface components (OICs) (not shown) that contain optical to electrical (O/E) and electrical to optical (E/O) converters (not shown), as will be described in more detail below. The OIMs 148(1)-148(N) support the radio bands that can be provided by the RIMs 142(1)-142(M), including the examples previously described above. Thus, in this embodiment, the OIMs 148(1)-148(N) may support a radio band range from 400 MHz to 2700 MHz, as an example.

The OIMs 148(1)-148(N) each include E/O converters to convert the downlink electrical communications signals 146D(1)-146D(R) into the downlink optical communications signals 150D(1)-150D(R). The downlink optical communications signals 150D(1)-150D(R) are communicated over a downlink optical fiber communications medium 152D to a plurality of remote antenna units (RAUs) 154(1)-154(S). The notation “1-S” indicates that any number of the referenced component 1-S may be provided. O/E converters provided in the RAUs 154(1)-154(S) convert the downlink optical communications signals 150D(1)-150D(R) back into the downlink electrical communications signals 146D(1)-146D(R), which are provided to antennas 158(1)-158(S) in the RAUs 154(1)-154(S) to client devices (not shown) in the reception range of the antennas 158(1)-158(S).

E/O converters are also provided in the RAUs 154(1)-154(S) to convert uplink electrical communications signals 160U(1)-160U(S) received from client devices through the antennas 158(1)-158(S) into uplink optical communications signals 150U(1)-150U(S) to be communicated over an uplink optical fiber communications medium 152U to the OIMs 148(1)-148(N). The OIMs 148(1)-148(N) include O/E converters that convert the uplink optical communications signals 150U(1)-150U(S) into uplink electrical communications signals 162U(1)-162U(S) that are processed by the RIMs 142(1)-142(M) and provided as the uplink electrical communications signals 162U(1)-162U(S). Note that the downlink optical fiber communications medium 152D and the uplink optical fiber communications medium 152U connected to each RAU 154(1)-154(S) may be a common optical fiber communications medium, wherein for example, wave division multiplexing (WDM) may be employed to provide the downlink optical communications signals 150D(1)-150D(R) and the uplink optical communications signals 150U(1)-150U(S) on the same optical fiber communications medium.

The interference signal offset circuits 30, 30(1), and 30(2) of FIGS. 2, 4, and 5, respectively, may be provided in an indoor environment, as illustrated in FIG. 7. FIG. 7 is a partially schematic cut-away diagram of an exemplary building infrastructure 170 in which an interference signal offset circuit, including the interference signal offset circuits 30, 30(1), and 30(2) of FIGS. 2, 4, and 5, respectively, can be employed. The building infrastructure 170 in this embodiment includes a first (ground) floor 172(1), a second floor 172(2), and a third floor 172(3). The floors 172(1)-172(3) are serviced by a central unit 174 to provide antenna coverage areas 176 in the building infrastructure 170. The central unit 174 is communicatively coupled to a base station 178 to receive downlink communications signals 180D from the base station 178. The central unit 174 is communicatively coupled to RAUs 182 to receive uplink communications signals 180U from the RAUs 182, as previously discussed above. The downlink and uplink communications signals 180D, 180U communicated between the central unit 174 and the RAUs 182 are carried over a riser cable 184. The riser cable 184 may be routed through interconnect units (ICUs) 186(1)-186(3) dedicated to each of the floors 172(1)-172(3) that route the downlink and uplink communications signals 180D, 180U to the RAUs 182 and also provide power to the RAUs 182 via array cables 188.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents. 

What is claimed is:
 1. An interference signal offset circuit in a distributed antenna system (DAS), comprising: at least one offset signal generation circuit configured to: receive a downlink signal in a downlink path, the downlink signal comprising at least one unwanted downlink interference signal; and generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal; a signal summing circuit configured to: receive an uplink signal in an uplink path, the uplink signal comprising a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; receive the at least one uplink interference offset signal; generate an output uplink signal based on the received uplink signal; and combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and a control circuit configured to: receive the output uplink signal from the signal summing circuit; and configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.
 2. The interference signal offset circuit of claim 1, wherein: the at least one unwanted downlink interference signal comprises a plurality of downlink intermodulation products; and the at least one offset signal generation circuit is configured to generate the at least one uplink interference offset signal based on at least one downlink intermodulation product among the plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.
 3. The interference signal offset circuit of claim 2, wherein the control circuit is further configured to: measure an interference signal power level of the at least one downlink intermodulation product among the plurality of downlink intermodulation products; measure an interference signal phase of the at least one downlink intermodulation product among the plurality of downlink intermodulation products; and configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal based on the measured interference signal power level and the measured interference signal phase.
 4. The interference signal offset circuit of claim 3, wherein the at least one offset signal generation circuit is configured generate the at least one uplink interference offset signal to substantially match the interference signal power level of the at least one downlink intermodulation product and be substantially opposite in phase to the interference signal phase of the at least one downlink intermodulation product.
 5. The interference signal offset circuit of claim 2, wherein the at least one uplink interference offset signal generated by the at least one offset signal generation circuit is configured to offset the at least one downlink intermodulation product among the plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.
 6. A method of offsetting at least one unwanted downlink interference signal from an uplink signal received in a distributed antenna system (DAS), comprising: receiving a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal; generating at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal; receiving an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; generating an output uplink signal based on the uplink signal; and combining the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal.
 7. The method of claim 6, further comprising generating the at least one uplink interference offset signal to offset at least one downlink intermodulation product among a plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.
 8. The method of claim 6, further comprising: generating the at least one uplink interference offset signal by at least one offset signal generation circuit; and combining the uplink signal with the at least one uplink interference offset signal by a signal summing circuit.
 9. The method of claim 8, further comprising receiving the uplink signal from a coupling device communicatively coupled to at least one antenna, wherein the coupling device is further configured to provide the downlink signal to the at least one antenna.
 10. The method of claim 9, further comprising: decoupling the at least one antenna from the coupling device; decoupling the at least one offset signal generation circuit from the signal summing circuit; receiving a downlink test signal in the downlink path, wherein the downlink test signal comprises a plurality of downlink test intermodulation products; receiving an uplink test signal in the uplink path, wherein the uplink test signal comprises the plurality of downlink test intermodulation products leaked from the downlink path to the uplink path; and measuring a first power level and a first phase of at least one downlink test intermodulation product among the plurality of downlink test intermodulation products.
 11. The method of claim 10, further comprising: decoupling the signal summing circuit from the coupling device; coupling the at least one offset signal generation circuit to the signal summing circuit; providing the downlink signal to the at least one offset signal generation circuit, wherein the downlink signal comprises a plurality of downlink intermodulation products; receiving at least one downlink intermodulation product among the plurality of downlink intermodulation products from the at least one offset signal generation circuit; and measuring a second power level and a second phase of the at least one downlink intermodulation product received from the at least one offset signal generation circuit.
 12. The method of claim 11, further comprising: adjusting the second power level of the at least one downlink intermodulation product to substantially match the first power level of the at least one downlink test intermodulation product; and adjusting the second phase of the at least one downlink intermodulation product to be substantially opposite of the first phase of the at least one downlink test intermodulation product.
 13. A remote antenna unit (RAU) in a distributed antenna system (DAS), comprising: a downlink power amplifier configured to amplify a plurality of downlink communications signals received in a downlink path to generate a downlink signal in the downlink path, the downlink signal comprising at least one unwanted downlink interference signal; at least one antenna configured to transmit the downlink signal and receive an uplink signal; a coupling device communicatively coupled to the downlink power amplifier and the at least one antenna, wherein the coupling device is configured to: distribute the downlink signal received from the downlink path to the at least one antenna for transmission; and distribute the uplink signal received from the at least one antenna to an uplink path, the uplink signal comprising a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; and an interference signal offset circuit, comprising: at least one offset signal generation circuit configured to: receive the downlink signal comprising the at least one unwanted downlink interference signal; and generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal; a signal summing circuit configured to: receive the uplink signal in the uplink path; receive the at least one uplink interference offset signal from the at least one offset signal generation circuit; generate an output uplink signal based on the received uplink signal and the received at least one uplink interference offset signal; and combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and a control circuit configured to: receive the output uplink signal from the signal summing circuit; and configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.
 14. The RAU of claim 13, wherein the coupling device is selected from the group consisting of: a duplexer; a multiplexer; a hybrid combiner; and a software-defined frontend module.
 15. The RAU of claim 13, wherein the at least one unwanted downlink interference signal comprises a plurality of downlink intermodulation products generated when the plurality of downlink communications signals is amplified by the downlink power amplifier to generate the downlink signal.
 16. The RAU of claim 15, wherein the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path by the coupling device comprises the plurality of downlink intermodulation products.
 17. The RAU of claim 15, wherein the at least one offset signal generation circuit is configured to generate the at least one uplink interference offset signal to offset at least one downlink intermodulation product comprised in the at least one unwanted downlink interference signal.
 18. The RAU of claim 15, wherein: the at least one offset signal generation circuit comprises a plurality of offset signal generation circuits disposed in a parallel arrangement, each of the plurality of offset signal generation circuits configured to receive the downlink signal; the at least one uplink interference offset signal comprises a plurality of uplink interference offset signals, each of the plurality of uplink interference offset signals configured to offset at least one downlink intermodulation product among the plurality of downlink intermodulation products.
 19. The RAU of claim 15, wherein the at least one offset signal generation circuit comprises: an intermodulation product filter configured to selectively pass at least one downlink intermodulation product among the plurality of downlink intermodulation products; an adjustable power amplifier coupled to the intermodulation product filter and configured to amplify the at least one downlink intermodulation product passing through the intermodulation product filter; and an adjustable phase shifter coupled to the adjustable power amplifier and configured to phase-shift the at least one downlink intermodulation product; wherein the at least one offset signal generation circuit is configured to provide the amplified and phase-shifted at least one downlink intermodulation product to the signal summing circuit as the at least one uplink interference offset signal.
 20. The RAU of claim 19, further comprising a first switch configured to couple the coupling device to the at least one antenna or decouple the coupling device from the at least one antenna.
 21. The RAU of claim 20, wherein the signal summing circuit comprises: a second switch configured to couple or decouple the signal summing circuit with the coupling device; a third switch configured to couple or decouple the signal summing circuit with the at least one offset signal generation circuit; a signal summing point coupled to the second switch and the third switch, wherein the signal summing point is configured to combine the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and an uplink power amplifier coupled to the signal summing point.
 22. The RAU of claim 21, wherein: the first switch is configured to decouple the coupling device from the at least one antenna; the second switch is configured to couple the signal summing circuit with the coupling device; the third switch is configured to decouple the signal summing circuit from the at least one offset signal generation circuit; the coupling device is further configured to: receive a downlink test signal comprising a plurality of downlink test intermodulation products; and provide the downlink test signal as an uplink test signal in the uplink path; the signal summing circuit is further configured to: amplify the uplink test signal; and provide the amplified uplink test signal to the uplink signal filter in the control circuit; and the control circuit comprises: an uplink signal filter configured to selectively pass at least one downlink test intermodulation product among the plurality of downlink test intermodulation products; a power detection circuit is configured to measure a first power level of the at least one downlink test intermodulation product passed through the uplink signal filter; and a controller is configured to receive the at least one downlink test intermodulation product from the power detection circuit and measure a first phase of the at least one downlink test intermodulation product.
 23. The RAU of claim 22, wherein: the second switch is configured to decouple the signal summing circuit from the coupling device; the third switch is configured to couple the signal summing circuit with the at least one offset signal generation circuit; the at least one offset signal generation circuit is configured to receive the downlink signal and the plurality of downlink intermodulation products comprised in the downlink signal; the controller in the control circuit is configured to configure the intermodulation product filter in the at least one offset signal generation circuit to pass the at least one downlink intermodulation product among the plurality of downlink intermodulation products, wherein the at least one passed downlink intermodulation product is in the same order as the at least one downlink test intermodulation product passed through the uplink signal filter in the control circuit; the power detection circuit in the control circuit is configured to measure a second power level of the at least one downlink intermodulation product passed by the intermodulation product filter in the at least one offset signal generation circuit; and the controller in the control circuit is further configured to: measure a second phase of the at least one downlink intermodulation product passed by the intermodulation product filter in the at least one offset signal generation circuit; adjust the adjustable power amplifier in the at least one offset signal generation circuit to make the measured second power level to substantially match the measured first power level; and adjust the adjustable phase shifter in the at least one offset signal generation circuit to make the measured second phase to be substantially opposite of the measured first phase. 